unit-testing.js

 it('should return objects', function () {

        var backend = { transfer: sandbox.stub() };
        var stub2 = sandbox.stub(repository, 'getMails').returns([
            {id: 123, to: 'peter.cosemans@gmail.com', body: 'aaaa...'},
            {id: 123, to: 'wim.vanhoye@euri.com', body: 'bbb...'}
        ]);

        mailSystem.transferEuriMails(backend);
        expect(stub2).to.have.been.called;
        var mails = stub2.returnValues[0][0];
        expect(mails).to.include.keys(['to', 'id', 'body']);
        expect(backend.transfer).to.have.been.called;

    });